Ramona Singer

Lesson to all would-be cheaters: If you're going to be unfaithful, don't let Patti Stanger see it.

On Thursday's Watch What Happens Live, the Millionaire Matchmaker star told a shocked Andy Cohen that she was a firsthand witness to Mario Singer stepping out on his now-estranged wife Ramona Singer.

Now, Stanger has exclusively talked to PEOPLE to fill in the details of the night when she "saw the whole thing go down." In fact, Stanger says she witnessed what she believes was the beginning of Mario's long-term affair with twenty-something Kyle "Kasey" Dexter.

The straight-talking, business-savvy brunette audiences grew to know and love – and some castmates learned to loathe – on the first three seasons of The Real Housewives of New York City is officially back for the show's seventh season, PEOPLE has confirmed.

"I'm excited," Frankel, 43, tells PEOPLE of her decision to return to reality TV, which she denied earlier this month. "It feels like the first season when it was fresh and new and unknown."

Carole Radziwill, Heather Thomson, Kristen Taekman, LuAnn de Lesseps, Ramona Singer and Sonja Morgan will be back, too, a rep for the show tells PEOPLE.

Mario Singer and Kyle "Kasey" Dexter looked "very flirty" at the Women's Health Party Under the Stars in Bridgehampton, New York, on Saturday night, an onlooker tells PEOPLE. The two were also photographed together in Sag Harbor.